Robert Love posted in his blog some interesting screenshots: Thanks to beaglefs, a FUSE-based filesystem written by him that creates a real filesystem subtree from the results obtained from a beagle query) he was able to get a "people" subdirectory, with subdirectories named as your contacts, icons, and inside every directory links to all the documents related with that contact.

I use Ubuntu, and I don't seem to find a way to build a query from Places > Search. All this does is open the standard Beagle window, which does not have a File menu.

Just to clarify: if you go Places > Search in the Gnome panel menu, it will indeed open your standard Beagle search.
But what I was referring to was going Places > Search in the menu of _any Nautilus window_, that's why i said as a first step to open any folder.
That's one more hint on how poor this current implementation is from a UI point of view is, as two identical menu titles and two identical menu items will lead to very different outcomes.

You should end up with the "query builder" you can see at http://www.gnome.org/~davyd/gnome-2-14/ under "Searching for Love". You didn't specify which Ubuntu release you're using but since the Beagle search is integrated, I assume it will be using Gnome 2.14?